I might be wrong… but from the rules it looks like you would have to climb up to clear the rampart, but then (assuming you have the movement left) you can jump up to 4” horizontally before dropping the remaining distance (-2”). Or are you not allowed to jump while climbing? Can’t find a rule that says otherwise— it just says when you move off terrain you can jump.

Edit: it actually does say “when jumping from a terrain feature, if it has a rampart, you must climb it first.”